• Journal of the Earthquake Engineering Society of Korea
• /
• v.17 no.6
• /
• pp.245-255
• /
• 2013

According to natural frequency of soil, characteristics of earthquake responses of an isolated containment building in nuclear power plants are examined. For this, earthquake response analysis of seismically isolated containment buildings in nuclear power plants is carried out by strictly considering soil-structure interactions. The structure and near-field soil are modeled by the finite element method while far-field soil by consistent transmitting boundary. The equation of motion of a soil-structure interaction system under incident seismic wave is derived. The derived equations of motion are solved to carry out earthquake analysis of a seismically isolated soil-structure system. Generally, the results of this analysis show that seismic isolation significantly reduces the responses of the soil-structure system. However, if the natural frequency of the soil is similar to that of the soil-structure system, the responses of the containment buildings in nuclear power plants rather increases due to interactions in the system.

• Structural Engineering and Mechanics
• /
• v.87 no.2
• /
• pp.173-189
• /
• 2023

For a given structural geometry, the stiffness and damping parameters of the soil and the dynamic response of the structure may change in the face of an equivalent linear soil behavior caused by a strong earthquake. Therefore, the influence of equivalent linear soil behavior on the impedance functions form and the seismic response of the soil-structure system has been investigated. Through the substructure method, the seismic response of the selected structure was obtained by an analytical formulation based on the dynamic equilibrium of the soil-structure system modeled by an analog model with three degrees of freedom. Also, the dynamic response of the soil-structure system for a nonlinear soil behavior and for the two types of impedance function forms was also analyzed by 2D finite element modeling using ABAQUS software. The numerical results were compared with those of the analytical solution. After the investigation, the effect of soil nonlinearity clearly showed the critical role of soil stiffness loss under strong shaking, which is more complex than the linear elastic soil behavior, where the energy dissipation depends on the seismic motion amplitude and its frequency, the impedance function types, the shear modulus reduction and the damping increase. Excellent agreement between finite element analysis and analytical results has been obtained due to the reasonable representation of the model.

• Structural Engineering and Mechanics
• /
• v.71 no.4
• /
• pp.445-458
• /
• 2019

This study mainly aims to assess the performance of soil-structure systems designed by direct displacement-based method coupled with strong column-weak beam design concept through various system identification techniques under strong ground motions. To this end, various system identification methods are employed to evaluate the dynamic characteristics of a structure (i.e., modal frequency, system damping, mode shapes, and plastic hinge formation pattern) under a strong seismic excitation considering soil-structure interaction for different site conditions as specified by ASCE 7-10. The scope of the study narrowed down to the code-complying low- to high-rise steel moment resisting frames with various heights (4, 8, 12, 16-story). The comparison of the result of soil-structure systems with fix-based support condition indicates that the modal frequencies of these systems are highly influenced by the structure heights, specifically for the softer soils. This trend is more significant for higher modes of the system which can considerably dominate the response of structures in which the higher modes have more contribution in dynamic response. Amongst all studied modes of the vibration, the damping ratio estimated for the first mode is relatively the closet to the initial assumed damping ratios. Moreover, it was found that fewer plastic hinges are developed in the structure of soil-structure systems with a softer soil which contradicts the general expectation of higher damageability of such structural systems.

• Geomechanics and Engineering
• /
• v.34 no.4
• /
• pp.437-447
• /
• 2023

Inclined piles are commonly used in civil engineering constructions where significant lateral resistance is required. Many researchers proved their positive performance on the seismic behavior of the supported structure and the piles themselves. However, most of these numerical studies were done within the framework of linear elastic or elastoplastic soil behavior, neglecting therefore the soil non-linearity at low and moderate soil strains which is questionable and could be misleading in dynamic analysis. The main objective of this study is to examine the influence of the pile inclination on the seismic performance of the soil-pile-structure system when both the linear elastic and the nonlinear soil models are employed. Based on the comparative responses, the adequacy of the soil's linear elastic behavior will be therefore evaluated. The analysis is conducted by generating a three-dimensional finite difference model, where a full interaction between the soil, structure, and inclined piles is considered. The numerical survey proved that the pile inclination can have a significant impact on the internal forces generated by seismic activity, specifically on the bending moment and shear forces. The main disadvantages of using inclined piles in this system are the bending forces at the head and pile-to-head connection. It is crucial to account for soil nonlinearity to accurately assess the seismic response of the soil-pile-structure system.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.18 no.3
• /
• pp.125-132
• /
• 2014

In this study, a series of dynamic centrifuge tests were performed for a soil-foundation-structural interaction system in dry sand with various embedded depths and superstructure conditions. Sinusoidal wave, sweep wave and real earthquake were used as input motion with various input acceleration and frequencies. Based on the results, a natural period and an earthquake load for soil-structure interaction system were evaluated by comparing the free-field and foundation accelerations. The natural period of free field is longer than that of the soil-foundation-structure system. In addition, it is confirmed that the earthquake load for soil-foundation-structure system is smaller than that of free-field in short period region. In contrast, the earthquake load for soil-foundation-structure interaction system is larger than that of free-field in long period region. Therefore, the current seismic design method, applying seismic loading of free-field to foundation, could overly underestimate seismic load and cause unsafe design for long period structures, such as high-rise buildings.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.09a
• /
• pp.184-191
• /
• 2010

This paper proposes the shaking table testing method for replicating the dynamic behavior of soil-structure interaction (SSI) system, without any physical soil model and only using superstructure model. Applying original SSI system to the substructure method produces two substructures; superstructure and soil model corresponding to experimental and numerical substructures, respectively. Interaction force acting on interface between the two substructures is observed from measuring the accelerations of superstructure, and the interface acceleration or velocity, which is the needed motion for replicating the dynamic behavior of original SSI system, is calculated from the numerical substructure reflecting the dynamic soil stiffness of soil model. Superstructure is excited by the shaking table with the motion of interface acceleration or velocity. Analyzing experimental results in time and frequency domains show the applicability the proposed methodologies to the shaking table test considering dynamic soil-structure interaction.

• Ocean Systems Engineering
• /
• v.9 no.3
• /
• pp.241-259
• /
• 2019

This paper presents a fully three-dimensional numerical approach for analyzing deepwater drilling riser-conductor system vortex-induced vibrations (VIV) including nonlinear soil-structure interactions (SSI). The drilling riser-conductor system is modeled as a tensioned beam with linearly distributed tension and is solved by a fully implicit discretization scheme. The fluid field around the riser-conductor system is obtained by Finite-Analytic Navier-Stokes (FANS) code, which numerically solves the unsteady Navier-Stokes equations. The SSI is considered by modeling the lateral soil resistance force according to nonlinear p-y curves. Overset grid method is adopted to mesh the fluid domain. A partitioned fluid-structure interaction (FSI) method is achieved by communication between the fluid solver and riser motion solver. A riser-conductor system VIV simulation without SSI is firstly presented and served as a benchmark case for the subsequent simulations. Two SSI models based on a nonlinear p-y curve are then applied to the VIV simulations. Also, the effects of two key soil properties on the VIV simulations of riser-conductor systems are studied.

• Geomechanics and Engineering
• /
• v.5 no.4
• /
• pp.283-297
• /
• 2013

The aim of this paper is to investigate how the soil-structure interaction affects sloshing response of the elevated tanks. For this purpose, the elevated tanks with two different types of supporting systems which are built on six different soil profiles are analyzed for both embedded and surface foundation cases. Thus, considering these six different profiles described in well-known earthquake codes as supporting medium, a series of transient analysis have been performed to assess the effect of both fluid sloshing and soil-structure interaction (SSI). Fluid-Elevated Tank-Soil/Foundation systems are modeled with the finite element (FE) technique. In these models fluid-structure interaction is taken into account by implementing Lagrangian fluid FE approximation into the general purpose structural analysis computer code ANSYS. A 3-D FE model with viscous boundary is used in the analyses of elevated tanks-soil/foundation interaction. Formed models are analyzed for embedment and no embedment cases. Finally results from analyses showed that the soil-structure interaction and the structural properties of supporting system for the elevated tanks affected the sloshing response of the fluid inside the vessel.

• Earthquakes and Structures
• /
• v.22 no.3
• /
• pp.219-230
• /
• 2022

Knowing that the variability of soil properties is an important source of uncertainty in geotechnical analyses, we will study in this paper the effect of this variability on the seismic response of a structure within the framework of Soil Structure Interaction (SSI). We use the proposed and developed model (N2-ISS, Mekki et al., 2014). This approach is based on an extension of the N2 method by determining the capacity curve of the fixed base system oscillating mainly in the first mode, then modified to obtain the capacity curve of the system on a flexible basis using the concept of the equivalent nonlinear oscillator. The properties of the soil that we are interested in this paper will be the shear wave velocity and the soil damping. These parameters will be modeled at first, as independent random fields, then, the two parameters will be correlated. The results obtained showed the importance of the use of random field in the study of SSI systems. The variability of soil damping and shear wave velocity introduces significant uncertainty not only in the evaluation of the damping of the soil-structure system but also in the estimation of the displacement of the structure and the base-shear force.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.17 no.2
• /
• pp.53-59
• /
• 2013

Several researches have been studied to enhance the seismic performance of nuclear power plants (NPPs) by application of seismic isolation. If a seismic base isolation system is applied to NPPs, seismic performance of nuclear power plants should be reevaluated considering the soil-structure interaction effect. The seismic fragility analysis method has been used as a quantitative seismic safety evaluation method for the NPP structures and equipment. In this study, the seismic performance of an isolated NPP is evaluated by seismic fragility curves considering the soil-structure interaction effect. The designed seismic isolation is introduced to a containment building of Shin-Kori NPP which is KSNP (Korean Standard Nuclear Power Plant), to improve its seismic performance. The seismic analysis is performed considering the soil-structure interaction effect by using the linearized model of seismic isolation with SASSI (System for Analysis of Soil-Structure Interaction) program. Finally, the seismic fragility is evaluated based on soil-isolation-structure interaction analysis results.